This invention relates to gauge hatches which reduce low level fugitive vapor emissions prior to opening.
At least one opening or vent is commonly provided in a tank (such as a reactor, a processing device, a storage tank, a gas holder or other vessel) for the discharge, or the release, of an undesirably large pressure differential relative to the adjacent environment. To regulate use or operation of the tank, avoid material loss from the tank, prevent damage to the tank, and/or minimize or even prevent environmental contamination with material from the tank, such a vent is commonly provided with a vent closure that can open at a preset pressure differential.
While various vent closure structures are known, one particularly effective structure utilizes a combination of pallet and diaphragm. The pallet in normal valve operation extends across and closes the vent mouth while the associated diaphragm seats about and seals the vent mouth. The pallet and diaphragm combination can be considered to comprise or to be included in a vent closure cover subassembly.
One commonly used type of vent closure structure that incorporates a pallet and diaphragm combination is a gauge hatch. Characteristically, a conventional gauge hatch has a radially extending pivot arm that is associated with an exterior central portion of the closure cover subassembly and that is pivotably associated with an exterior cover-adjacent hitching or pivot post. Thus, this pivot arm permits the normally closed cover subassembly to be pivoted to a vent open position where the cover assembly and pivot arm do not interfere with tank interior access for tank measurements that are made through a vent by an operator. The cover subassembly in a gauge hatch thus can be assembled so as to be either opened manually by the operator, or opened automatically if the associated tank reaches a set pressure where pressure in the tank needs to be relieved.
Various means are known for regulating the opening or set pressure in a gauge hatch-equipped vent where, at vent opening, the pallet and diaphragm combination separate from the valve mouth. For example, one particularly effective pressure regulating means comprises a weight that is inherently associated with, or that is effectively loaded onto the upper outside surface of the cover. Thus, in such an arrangement, the weight-loaded pallet and diaphragm combination of a cover separates from its associated seated configuration at a preset tank pressure (which can be super-atmospheric), thereby to achieve vent closure opening.
Some gauge hatches are provided with retainer means for optionally holding the closure cover subassembly in a xe2x80x9cbolted downxe2x80x9d or equivalent vent closed configuration. The use of the retainer means can be an operator-selected option. Such a gauge hatch is typically utilized for association with a tank that is also equipped with a vent valve which automatically opens when the associated tank reaches a set pressure.
One problem with such a pallet and diaphragm-type gauge hatch is that a small volume of fugitive vapor emissions (typically parts per million) may occur between the diaphragm and its seat before either the set opening pressure of the gauge hatch cover is reached or the gauge hatch cover is manually opened by an operator.
The present invention overcomes this fugitive emissions problem for pallet and diaphragm type gauge hatch vent closures by incorporating into the gauge hatch structure a cooperating liquid seal. The liquid seal can function to virtually eliminate the escape of all fugitive vapor emissions prior to the opening of the pallet and diaphragm combination either at a set opening pressure or at manual opening.
More particularly, this invention relates to a gauge hatch structure for a tank vent or the like comprising an integrated combination of (a) a normally pressure responsive vent closure cover means that incorporates a pallet means with (b) a pressure-responsive liquid seal.
The inventive gauge hatch structure incorporates a cover subassembly, a cooperating vent neck and wall means that along with the neck define a reservoir. In the cover subassembly, the pallet means normally closes the neck upper end. Preferably the pallet means in the cover assembly is also associated with a diaphragm that is normally seated at the vent neck upper end portion. A flange-type mounting means for associating the gauge hatch with a tank or the like is also incorporated. Depending upon the arrangement of the components employed in a particular embodiment of the gauge hatch structure, the inventive gauge hatch structure can be used either for relief of pressure in a tank holding super-atmospheric pressures, or as a manually operable vent port for use in tank measurements or the like. (The term xe2x80x9cmanuallyxe2x80x9d or equivalent is used in a generic sense to indicate operation by a user or operator using a hand or a foot.)
The gauge hatch cover subassembly and the liquid seal subassembly operate cooperatively. The combination functions so that the liquid seal subassembly can eliminate the escape into the environment of low level fugitive vapor emissions past the pallet and also the diaphragm seat (if present) prior to the gauge valve cover subassembly opening either at a set pressure or manually.
In addition, the inventive gauge hatch structure includes an arm means that preferably radially extends across at least a portion of the closure cover. A proximal portion of this arm means is preferably located at a central outside top portion of the cover means and fastening means interconnects these respective portions. A distal portion of this arm means is preferably located along the outside perimeter of the cover means where pivotal connecting means is provided. Thus, in the vent open configuration, the cover means can be pivoted upwardly and away from the vent neck upper end portion so as to be generally and preferably inclined relative thereto.
The arm means, the fastening means and the pivotal connecting means can have various structures. For example, the arm means can include an optional extension that extends from the cover central portion to an opposite side position (relative to the distal pivotal portion). In addition, retainer means can optionally be provided for operator-selected usage in holding the gauge valve cover means in a closed position with the pallet and the diaphragm (if present) seated and sealed upon the vent neck upper end portion.
Either the inherent weight of the closure cover means, or the effective auxiliary equivalent weight exteriorly applied to the closure cover means in combination with the inherent weight of the closure cover means, determines the set point opening pressure of the cover means even when the retainer means is present but is not operative or functional.
To facilitate manual opening and closing of the cover means, the arm means can include, if desired, auxiliary member means, such as an upstanding foot treadle or the like, to facilitate the manual opening and closing of the cover means by an operator.
In the inventive gauge hatch, the liquid seal subassembly includes a sealing liquid reservoir with a normally closed chamber that is located over a portion of the surface of a sealing liquid in the reservoir and that is radially adjacent to the vent neck. A side wall region of the closed chamber is defined by a baffle or apron that circumferentially extends around the vent neck and that is suspended preferably vertically from the pallet means. The apron extends down into the reservoir and has a lower end region that normally terminates below the surface of the sealing liquid in the reservoir.
When the inventive gauge hatch structure is adapted for use with a tank holding super atmospheric pressures, the reservoir is preferably circumferentially positioned about the outside of the vent neck, and any small volume of fugitive vapor emissions that leaks past the contact seal existing at the normally closed seat between the vent neck and the pallet (and, if present, also the diaphragm) enters the closed chamber. The liquid seal between the reservoir liquid and the apron lower end region does not allow vapor emissions that enter the closed chamber to escape and reach the atmosphere (that is, the environment).
The opening of the pallet and associated diaphragm at a set point pressure is independent in operation from the opening of the liquid seal. If and when the leakage of fugitive vapor emissions increases (perhaps caused by tank pressure increase), the pressure in the closed chamber increases. The increase causes the reservoir liquid in the closed chamber to be displaced downwardly and to move into an adjacent reservoir region, but the seal is maintained. Eventually the pressure can increase to a level which is in excess of the maximum displacable liquid head in the closed chamber. This level defines the maximum liquid seal pressure of the closed chamber.
In the inventive gauge hatch structure, the cover means preferably incorporates a combination of diaphragm and associated pallet. The cover means preferably lifts (that is, opens and separates) from the neck-associated seating surface at a set point pressure which is preferably at or below the maximum liquid seal holding pressure. Preferably, the inventive gauge hatch structure is leak-free until the cover means lifts from the seat at the neck either at a set point or manually.
The inventive gauge hatch structure can optionally be associated with various auxiliary subassemblies, such as a constant level sealing liquid supply source, and/or a signaling device (which preferably can be remotely sensed).
The set pressure opening of the cover subassembly is based upon the tank pressures applied to the cover structure. When such opening occurs, the apron is separated from the reservoir sealing liquid and tank pressure is vented to the atmosphere.
Various features of the inventive gauge hatch structure are discussed and disclosed in the following description.